Copper ropes
Copper ropes used in water-cooled cables of melting furnaces are made of twisted copper filaments. The used material, thickness and flexibility of the filaments, covering and their cross-section are main parameters for the cables which is discussed below, thoroughly.
Cable material (grade)
The copper ropes are of ETP grade copper under ASTM-C11000 standard. According to the standard the purity of this type is 99.95% and its conductance is at least 100% of the predefined base value designated by IACS (Annealed copper standard) which is 58 MΩ/m.
Thickness of the filaments
Against the filaments of the normal cables with thickness of 0.2 mm, the filaments used here should be thicker. Otherwise, by time passing, some of the filaments in the strands will tear off by the tension caused by cable movement and mechanical strokes and against its appearance, the cable’s resistance will increase by time.
Below table shows the suggested thickness for the filaments of the water-cooled cables:
| type | Thickness |
|---|---|
| secondary cables | 0.25 mm |
| Hydroelectric cables used in induction furnaces | 0.40 – 0.45 mm |
| Hydroelectric cables used in electric arc furnaces and crucibles | 0.50 – 0.60 mm |
Flexibiliy
The flexibility of the cooper ropes in the water-cooled cables is worth noting. Low flexibility will result in torn filamnets caused by mechanical tensions and strokes like using thin filaments. Hence the copper ropes should be annealed.
Covering type
Filaments of the cables are used in both bare and tin coated form. Tin coated strands are more resilient against chemical erosion caused by water contact. It is obvious with low quality water, will cause chemical reaction on the surface of the filaments heated by electric current and consequently will change color and ultimately be torn. But it should be mentioned that tin coated strands are considerably more expensive than the uncoated ones and when the quality of the water and physical conditions of the cables are not so harsh, using tin coated strands are not much suggested.
Since the water-cooled cables of the arc and laddle furnaces are in continous movement, to avoid strands from scratching together during sudden movements, perferably the outer surface of the cables are covered with a special coverage fully or every other one.
These covers are made of LSOH (low-smoke and halogen-less rubber) same as the black material used to cover simple cables which under high temratures and while brning will not make much smoke and also no poisenous gases. İn order o avoid stopping water between strands and for better heat mitigation, these covers are manufactured in punched form.
Cross-section
One of the most important parameters of the strands in the water-cooled cable, is the cross-section, number and the composition of the filamnets. The cross section is chosen related to the allowed current density which is 10 t0 15 A/mm2 for induction furnaces and around 4.5 to 6 A/mm2 for arc furnaces becuase of the sudden peaks and high transient currents.
Beside cross-section, number and the composition of the filaments are chosen according to ASTM-b172 standard like below table:
|
Actual cross section (mm2)
|
Combination of
single courses |
The thickness of single strands (mm)
|
Nominal cross- sectional area (mm2)
|
|
|---|---|---|---|---|
| 26 | 19 × 28 | 0.25 |
25 |
Used to make Alexander
hydroelectric cables
|
| 22 | 7 × 25 | 0.40 |
Used for making induction furnace cables (IF) |
|
| 50 | 19 × 21 | 0.40 | 50 | |
| 100 | 19 × 33 | 0.45 | 100 | |
| 193 | 7 × 7 × 20 | 0.50 | 200 |
It is used for the construction of hydroelectric cables of electric arc furnaces and patili (EAF & LF) |
| 392 | 19 × 7 × 15 | 0.50 | 400 | |
| 496 | 19 × 7 × 19 | 0.50 | 500 |
Another noteworthy point is the direction of the twisted strands. To avoid loosening, the strands must be twisted in opposite direction.